Couldn't change sampling frequency when using Timer + PPI with ADC.

RE: Couldn't change sampling frequency when using Timer + PPI with ADC.

Alisha — Wed, 25 Apr 2018 14:03:22 GMT

Thanks for you reply, I use the same approach currently.

RE: Couldn't change sampling frequency when using Timer + PPI with ADC.

MartinBL — Wed, 25 Apr 2018 13:26:24 GMT

As you said yourself, you can only reach a sampling period of 2.09 seconds (~0.48 Hz). You are not able to scale the TIMER frequency below 31.25 kHz and the counter register is too small. You either need to use timer interrupts (trigger interrupt every 2 sec e.g. and count to 5) or the RTC.

RE: Couldn't change sampling frequency when using Timer + PPI with ADC.

Alisha — Wed, 25 Apr 2018 12:53:03 GMT

Thanks for your reply. Would you please explain how should I set timer setting for 0.1 Hz sampling with TIMER2 peripheral, I don't want to use RTC timer?

RE: Couldn't change sampling frequency when using Timer + PPI with ADC.

MartinBL — Wed, 25 Apr 2018 12:33:03 GMT

That sounds right. Maybe you can look into using the RTC instead. You can still use PPI and you should be able to achieve 0.1 Hz sampling.

RE: Couldn't change sampling frequency when using Timer + PPI with ADC.

Alisha — Wed, 25 Apr 2018 11:14:47 GMT

It seems I found the problem, the timer bit width is 16 bit and I try to set the ADC_SAMPLE_RATE to 10 second. Also the frequency of timer is 31.25 kHz, with simple computation the maximum possible delay is 2^16 / 31250 = 2.09 seconds. Am I right?